Centrifugal compressors are used to circulate refrigerant in a chiller via a refrigerant loop. Centrifugal compressors operate efficiently before reaching a condition known as surge. During surge, however, the compressor experiences too low a flow rate for a given pressure ratio, and may experience flow reversal.
In one example compressor, an impeller is supported on a rotor shaft by magnetic bearings. Vibrations detected by the magnetic bearing control systems have been used to detect instability in the fluid caused by stall and surge conditions. These vibrations have been used to regulate the flow through the impeller by adjusting inlet guide vanes.
In another example, pressures are measured at either side of an impeller. An undesired pressure fluctuation at a given operating condition indicates flow instability, which generates shaft instability. In this example, a position of a variable geometry diffuser is adjusted to regain flow stability.